The present invention relates to an airbag for protecting the head of an occupant, and particularly to a head-protecting airbag which inflates over the side window of a side door inside a vehicle in the event of rollover or a side impact. The present invention also relates to a head-protecting airbag device including such a head-protecting airbag.
Airbags for protecting the heads of vehicle occupants are installed near the corners between the roof and the lateral surfaces inside the vehicle. These airbags are inflated over the window of a side door by gas introduced through a gas inlet.
Japanese Unexamined Patent Application Publication No. 2001-328503 (incorporated by reference herein) discloses an airbag having a primary chamber and a secondary chamber. In the airbag according to this Japanese Unexamined Patent, gas discharged from a gas generator is introduced into the primary chamber. When the internal pressure of the primary chamber reaches a predetermined value, a tear seam breaks to transfer the gas from the primary chamber into the secondary chamber.
As shown in FIG. 7 of Japanese Unexamined Patent Application Publication No. 2001-328503, the internal pressure of the chambers changes suddenly when the tear seam breaks.
Accordingly, there remains a need for a head-protecting airbag and a head-protecting airbag device that exhibit a gentle change in internal pressure of the chambers and facilitate the adjustment of the internal pressure of the primary chamber.